This invention relates to a device for lifting a bottom side wall of a tyre in a tyre removing machine (in particular in a tyre removing machine where the tyre to be removed is positioned with its axis vertical).
The invention also relates to a tyre removing machine comprising this device.
The invention also relates to a method for removing tyres from wheels in a tyre removing machine comprising this device.
This invention can therefore be applied in the technical field of apparatus for mounting and, more specifically, for removing the tyres of automobiles, motorcycles, or other vehicles, from the respective wheel rims.
This specification refers only to the tyre removal procedure since the device according to the invention applies essentially to the step of taking the tyre off the rim.
More specifically, the invention relates to the procedure for extracting the bottom portion (that is, the bottom bead) of a tyre from the rim in a tyre removing machine adapted to support the wheel concerned with its axis extending vertically.
In light of this, prior art tyre removal machines comprise a horizontal turntable on which the wheel is positioned in such a way that its central axis is substantially vertical.
In this specification, the term wheel is used to mean an assembly of a tyre and a rim.
Once positioned on the turntable, the tyre has a bottom side wall facing the turntable itself and a top side wall facing upwards.
Each of the two side walls comprises a bead, that is to say, the reinforced edge of the tyre in contact with the rim.
The bead of the top side wall will hereinafter be referred to as the top bead and, similarly, the bead of the bottom side wall will hereinafter be referred to as the bottom bead.
In the same way, the rim edge which, once the tyre has been mounted, is in contact with the top bead will hereinafter be referred to as the top edge, while the edge that is in contact with the bottom bead will hereinafter be referred to as the bottom edge.
The removal procedure comprises a bead loosening step, that is, a step of disengaging the beads from the rim, and a step of positioning and locking the wheel on the turntable. This is followed by a step of extracting the tyre, where the top bead and the bottom bead are disengaged from the rim, enabling the tyre to be removed completely.
Prior art devices for pressing the beads of a tyre comprise two operating units, each acting on a respective side wall of the tyre in order to separate it from the edge of the rim.
This allows a tool to be inserted between the respective bead and the rim in a working step (where the wheel is made to rotate about its axis).
More specifically, a top operating unit acts on the top bead during both the mounting and the removal procedure, while a bottom operating unit acts on the bottom bead only during the removal procedure.
In particular, the top operating unit is used to push the top side wall of the tyre downwards in such a way as to create a space between the top edge of the rim and the top bead of the tyre to facilitate insertion of the removing tool.
Further, the top operating unit is used to keep the top bead of the tyre inside a suitable groove formed in the rim, commonly known as channel, and to reduce stress on the bead during mounting and removal.
The bottom operating unit is activated during tyre removal.
More specifically, the bottom operating unit is used after the top bead has been extracted.
More in detail, the bottom operating unit is used to lift the tyre until the bottom bead of the tyre is near the top edge of the rim.
Since that operating unit is used to lift the tyre, it will be referred to as lifting device.
In detail, a prior art lifting device for lifting the bottom side wall of a tyre typically comprises an arm pivoted to the frame of the tyre removing machine and designed to be moved by an operator between a rest position, where the arm is distal from the tyre, and an operating position, where the arm is proximal to the tyre.
There is also a disc rotatably associated with the end of the arm opposite the end that is pivoted to the frame of the tyre removing machine.
The disc lies in a substantially horizontal plane so that when the arm is in the operating position the disc is positioned under the bottom side wall of the tyre.
When the arm is in the operating position, since it is movable vertically, the disc, which is held in place manually by an operator, presses against the tyre's bottom side wall, thus lifting the bottom bead from the rim and allowing a removing tool to be inserted between the bottom bead itself and the top edge of the rim.
Prior art devices also have a metal bar that can be engaged with the arm of the lifting device at a recess formed in the arm itself so that the leverage effect can be used to facilitate the operator's task of pushing the arm against the tyre.
Disadvantageously, however, an operator using a prior art device needs both hands to press the arm of the device against the tyre and at the same time keep the tyre in place on the turntable (by acting manually on the outer portion of the tyre's circumference at a position diametrically opposite the side wall lifting disc).
This disadvantage is worsened especially when the tyre to be removed is very large since the two hands have to work on substantially opposite sides of the tyre.
Moreover, the use of the metal bar as described, is not only extremely awkward for the operator but is also potentially dangerous.
A technical solution is known from document EP1155880, that shows a machine for mounting and dismounting tyres of motor vehicle wheels, which comprises a frame rigidly connected to a support, rotating around a vertical axis, on which can be fixedly placed a rim of the wheel.
Said machine further comprises a couple of telescopic arms, a lower one and an upper one, connected to the frame and both rotatable around respective horizontal axis in order to respectively approach or move away.
The machine according to this solution allows to set the angle of the arms using hydraulic or pneumatic means in order to adapt the position of a tool to a tyre bead.
A further solution is known from document EP0499825.
This solution is similar to the previous one but it further shows the telescopic arms rotating around an axis parallel the wheel axis.
However, in this solution the arms have to be kept in the right angular position from the user by hand, introducing all the drawbacks previously discussed.
A different solution is shown in document EP0243785, that shows a machine for mounting and dismounting tyres of motor vehicle wheels, having a rotating support on which can be placed a wheel with its axis in a vertical position.
The rotating support is placed below a bridge shaped frame, which has a crosspiece on which is mounted a couple of arms.
Said arms are movable in mutual approach or separation around respective horizontal axis.
Moreover, a linear actuator is active on the rotating support for moving it upwardly or downwardly in order to press or lift the tyre bead.
However, this solution is clearly bulky and difficult to realize since it needs a lot of free space to place the bridge shaped frame.